The major objective of our research is to understand mechanisms of regulating undesirable B cell responsiveness, such as the humoral response to HIV which facilitates entry of the virus into monocytes (a process which could contribute to the pathogenesis of AIDS) or enhancing antibody against neoplastic cells that could lead to increased tumor growth. During the past grant period, we analyzed B cell unresponsiveness induced by exposure to haptenated gamma globulin conjugates as a model for tolerance. Recently, we extended this model to a novel system involving the pretreatment of murine spleen cells with anti-immunoglobulin (Ig) antibody, as surrogate antigen, for 24 hours before challenge with specific antigen or lipopolysaccharide (LPS). This protocol allows us to separate the inductive events from challenge, in analogy to tolerance protocols; moreover, in this system we can expose all B cells to the same (surrogate) antigen under defined conditions. Pretreatment of normal adult B cells with anti-Ig led to significant impairment of IgM and IgG antibody formation to both specific and polyclonal challenge, with the greatest reduction in the latter. This system will be analyzed in order to understand the mechanisms for the downregulation of B cell differentiation and the requirement for cell cycle progression out of G(o) into G(1) for negative signalling. Using abortive stimuli for cycle progression, we will determine whether anti-Ig signals need to be delivered at a critical point or if abortive entry into cycle without a second signal is required for tolerance. We also wish to establish the sensitivity of B cell subsets to negative signalling using different antigens, as well as defined B cell populations and a unique B cell lymphoma, CH12. In addition, we will establish whether clonally expanded B cell lines, CD5+ (Ly1) B cells, and immature developing bone marrow B cells can be regulated in the same manner. The phenotype of pretreated, unresponsive B cells and the effects of recombinant lymphokines, some of which we have shown prevent growth inhibition of B cell lymphomas, will also be examined. These studies interface with our continuing efforts to understand the mechanism of control of normal and neoplastic growth and the molecular and cell surface events involved in the regulation of differentiation of normal and transformed lymphocytes. Since HIV has recently been shown to enter monocytes via immune complex binding to Fc receptors, our studies are timely and important in providing a model for understanding the control of this undesirable humoral response, designing new modalities of vaccine therapy, as well as obviating responses that interfere with effective cellular immunity in cancer. These studies should lead next to manipulation of the responsiveness of human peripheral blood lymphocytes in SCID recipients.